Flexible packaging printing inks are typically printed by rotary letterpress printing using flexible rubber plates or by gravure printing using engraved chrome-plated cylinders on a wide variety of substrates, e.g. plastic films such as cellulose acetate, polyethylene, polyethylene terephthalate, polyesters, polystyrene, cellophane, glassine, tissue, aluminum foils, liners, bags, paper labels, box coverings, gift wrappings, etc.
Flexible packaging printing inks are widely used in the graphic arts industry. They offer economy, versatility; quality and simplicity and permit a roll of material to be multi-color printed in a continuous web at speeds of over 300 meters per minute and feed it directly to converting machines for slitting, forming or laminating. However, these inks must be carefully formulated so as to avoid the problems indigenous to these types of inks, e.g. chemical pinholing (failure of the ink to properly wet a plastic film surface), mechanical pinholing (the appearance of the pattern of the etched ink form roller), feathering (the appearance of stringy or ragged edges), mottle (ridged or speckled patterns), precipitation of part of the vehicle, blocking (a sticking or transfer of the image to the underside of the web), adhesion of the ink to the substrate, etc.
U.S. Pat. No. 5,338,785 (Catena et al.) discloses a flexible packaging printing ink is formulated from a copolymer of polyethylenene glycol methacrylate and a polyamide resin, pigment, solvent and cellulose acetate butyrate. The polyamide resin is prepared by condensing a dibasic acid mixture with a diamine mixture. The dibasic acid mixture comprises about 0.5 to 0.8 equivalents of a C.sub.20 -C.sub.44 dibasic acid mixture comprised of about 60 to 100% dimers, 0 to 40% trimers and 0 to 5% monomers, and about 0.2-0.7 equivalents of at least one C.sub.6 -C.sub.12 dibasic acid such as azelaic acid and adipic acid, while the diamine mixture comprises about 0.5-0.8 equivalents of piperazine or a substituted piperazine and the balance comprises at least one C.sub.2 -C.sub.12 alkyl diamine such as ethylene diamine.
The use of acrylate ester polymers as printing ink vehicles is generally discussed in "Printing Ink Vehicles", Encyclopedia of Polymer Science and Engineering, vol. 13, pp. 368-398 (John Wiley & Sons, Inc. N.Y., N.Y., 1988). For example, at page 393, it is stated that while acrylis and methacrylic ester resins are used in water-based systems, several problems still exist, for example balancing water solubility in the ink and water resistance in the end product.
U.S. Pat. No. 5,075,364 (Phan et. al.) discloses a blend of a water-dissipatable polyester material, an acrylic polymer and a water-dissipatable vinyl polymer. It is stated that the acrylic polymer and the vinyl polymer must be compatible with the polyester which has a particular composition. It is stated that the polymer blends are useful for preparing ink compositions having improved block resistance, water resistance, and alcohol resistance.
U.S. Pat. No. 4,921,899 discloses an ink composition containing a blend of a polyester, an acrylic polymer and a vinyl polymer. The water-based inks containing the blend of these polymers as a binder can significantly improve ink film properties such as alcohol resistance, block resistance and water resistance as compared to use of water-dispersible polyester alone. The polymer blends were also employed to prepare ink primers and overprint varnishes. It is stated that these polymer blends were prepared by mixing an aqueous polyester dispersion with an acrylic emulsion which contains surfactants and other additives and that the presence of surfactants in the ink formulations creates several problems related to ink stability, printing process and print quality of the ink film.